The present invention relates generally to air intakes for aircraft engines, and, more specifically, to an air intake including new and improved means for bleeding intake airflow flowing near a duct wall.
The present invention has utility, for example, in a turboprop gas turbine engine wherein a propeller blade row is disposed coaxially with a gas turbine engine. In this arrangement, the air inlet of the engine may be made fully annular and disposed downstream of the propellers.
A measure of performance of a propeller system is represented by pressure recovery to the inlet, which is defined as the local pressure immediately downstream of the propellers, which includes pressure rise due to the work performed thereby, divided by the total pressure of the inlet ambient air. Pressure recovery to the inlet characterizes the air being provided to the air intake of the engine and a value thereof of about 1.05 is considered good performance. The pressure recovery, of course, varies from the root to the tip of the propeller blades and has undesirably low values near the root of the propeller blades.
In conventional turboprop aircraft engines the propeller centerline is offset from the centerline of the engine and an offset air inlet is utilized. This inlet is disposed at a relatively large radial distance from the propeller hub and therefore does not ingest undesirable propeller hub airflow, which results in relatively low values of pressure recovery. However, when a fully annular air inlet is utilized, the undesirable propeller hub airflow must necessarily be channeled into the air inlet, thus reducing the maximum potential performance of the engine.